In a motor, a direction of an electric current passing through a coil of each of coil units is switched, so that a rotor having a permanent magnet, which faces magnetic pole teeth of stator yokes, can be rotated. The coils are electrically connected to a motor circuit board so as to control the current direction passing through the coils, etc. For example, in an ordinary brushless motor, a magnet wire is wound, on an iron core of a stator, in a direction parallel to an output shaft (i.e., an axial direction of the coil is perpendicular to that of the stator), and ends of the magnet wire of the coil are extended, in the axial direction, and connected to a drive circuit.
In a stator unit of an inner rotor-type PM stepping motor, a magnet wire is wound on coil bobbins, each of which is formed around each of magnetic pole teeth of a stator yoke, and an inner end and an outer end of a coil are extended to a space formed on the outer side of the stator and electrically connected to a connector or a printed circuit board by lead terminals (see Japanese Laid-open Patent Publications No. 2002-78268 and No. 2005-110377).
In a stator unit of an outer rotor-type PM stepping motor, a magnet wire is wound on coil bobbins, each of which is provided on the inner side of each of magnetic pole teeth of a stator yoke. A guide section is provided between an inner part of the coil bobbin and an outer circumference of a bearing housing, and coil leads are passed through the guide section, so that ends of a coil can be electrically connected to a connector or a printed circuit board (see Japanese Laid-open Patent Publication No. 2007-49844).
In comparison with the inner rotor-type PM stepping motor, the outer rotor-type PM stepping motor having the same size is capable of generating greater torque. However, the coil leads must be wired in an inner space of the motor, it is difficult to sufficiently secure the inner space for wiring the coil leads. Since the coil leads must be wired in a tight space, wiring efficiency must be lowered and enough insulation reliability between the stator yoke and the coil cannot be secured.
On the other hand, lamination factor of the coil is lowered or cubic volume of the stator yoke constituting a magnetic path is reduced so as to secure enough working space for wiring the coil leads. In this case, performance of the motor must be worsened.
Namely, it is difficult to produce a large torque motor whose structure has high insulation reliability. Further, efficiency of assembling the outer rotor-type PM stepping motor is low, so it is difficult to expand use of said motor.